Inotropic Agents

Inotropic agents, or inotropes, are medicines that change the force of your heart’s contractions. There are 2 kinds of inotropes: positive inotropes and negative inotropes. Positive inotropes strengthen the force of the heartbeat. Negative inotropes weaken the force of the heartbeat.

Why do I need inotropes?

Both kinds of inotropes are used in the treatment of many different cardiovascular conditions. The kind of inotrope you are given depends on the condition you have.

Positive inotropes strengthen the heart’s contractions, so it can pump more blood with fewer heartbeats. This medicine is usually given to patients with congestive heart failure or cardiomyopathy. These medicines may also be given to patients who have had a recent heart attack. In some cases, inotropes are given to patients whose hearts have been weakened after heart surgery (in cases of cardiogenic shock).

Negative inotropes weaken the heart’s contractions and slow the heart rate. These medicines are used to treat high blood pressure (hypertension), chronic heart failure, abnormal heart rhythms (arrhythmias), and chest pain (angina). They are sometimes used in heart attack patients to reduce stress on the heart and prevent future heart attacks.

How do inotropes work?

Positive and negative inotropes work in different ways.

Positive inotropes help the heart pump more blood with fewer heartbeats. This means that although the heart beats less, it also beats with more force to meet the oxygen demands of your body.

For example, one kind of positive inotrope called digoxin strengthens the force of the heartbeat by increasing the amount of calcium in the heart’s cells. (Calcium stimulates the heart to contract.) When the medicine reaches the heart muscle, it binds to sodium and potassium receptors. These receptors control the amount of calcium in the heart muscle by stopping the calcium from leaving the cells. As calcium builds up in the cells, it causes a stronger force of contraction.

Negative inotropes include beta-blockers, calcium channel blockers, and antiarrhythmic medicines and they all work in different ways:

Beta-blockers “block” the effects of adrenaline on your body’s beta receptors. This slows the nerve impulses that travel through the heart. As a result, your heart does not have to work as hard because it needs less blood and oxygen. Beta-blockers also block the impulses that can cause an arrhythmia.

Calcium channel blockers slow the rate at which calcium passes into the heart muscle and into the vessel walls. This relaxes the vessels. The relaxed vessels let blood flow more easily through them, thereby lowering blood pressure.

Antiarrhythmic medicines slow the electrical conduction in the heart.

How much do I take?

There are many different kinds of inotropes. The amount of medicine you need to take may vary. Talk to your doctor or pharmacist for more information about how and when to take this medicine.

What if I am taking other medicines?

Other medicines that you may be taking can increase or decrease the effect of inotropes. These effects are called an interaction. Be sure to tell your doctor about every medicine and vitamin or herbal supplement that you are taking, so he or she can make you aware of any interactions.

The following are some of the medicines that can interact with inotropes. Because there are so many kinds of medicines within each category, not every type of medicine is listed by name. Tell your doctor about every medicine that you are taking, even if it is not listed below.

• Cholesterol-lowering medicines
• Diet pills
• Laxatives or anti-diarrhea medicines
• Antacids that contain aluminum or magnesium
• Over-the-counter medicines for cough, cold, or flu
• Over-the-counter medicines for hay fever or sinusitis
• Over-the-counter eye drops for red or bloodshot eyes

You should limit drinking grapefruit juice when you are taking inotropes. Grapefruit juice interferes with the liver’s ability to rid your body of some substances. This could lead to a buildup of inotropes in your body. Consult with your doctor about your dosage and the consumption of grapefruit.

You should also avoid alcohol and beverages that contain caffeine, such as coffee, tea, and soft drinks.

You should not take positive inotropes if you are already taking negative inotropes, such as beta-blockers, calcium channel blockers, or antiarrhythmics, unless your doctor has prescribed both. These medicines can be taken together, but only your doctor can prescribe the right balance of each.

What else should I tell my doctor?

Talk to your doctor about your medical history before you start taking inotropes. The risks of taking the medicine need to be weighed against its benefits. Here are some things to consider if you and your doctor are deciding whether you should begin taking inotropes.

• You have aortic stenosis.
• You have bradycardia (a very slow heart rate). Certain types of inotropes, especially digoxin, should not be used unless you have a pacemaker.
• You are pregnant or are thinking of becoming pregnant.
• You are breastfeeding.
• You have kidney or liver disease.
• You have thyroid disease.

What are the side effects?

Sometimes a medicine causes unwanted effects. These are called side effects. Not all of the side effects for inotropes are listed here. If you feel these or any other effects, you should check with your doctor.

• Low blood pressure (hypotension)
• An irregular heartbeat that causes dizziness, the feeling that your heart has skipped a beat (palpitations), shortness of breath, sweating, or fainting
• Trouble with your eyesight, such as blurry eyesight, double vision, or seeing yellow, green, or white halos around objects
• Dizziness or lightheadedness
• Headache
• A loss of appetite or an upset stomach
• Fatigue
• Throwing up
• Diarrhea
• Erectile dysfunction
• Breast enlargement in men
• Decreased sex drive
• Skin rash or hives
• Eye sensitivity to light
• Nosebleeds and bleeding gums

Many of these side effects are rare. Tell your doctor right away if you have any of these side effects. Do not stop taking your medicine unless your doctor tells you to. If you stop taking your medicine without checking with your doctor, it can make your condition worse.

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